The invention relates to the application of thresholds in light microscopy.
Light microscopy images may be automatically scanned to detect the presence of certain classes of objects, which may be distinguished from other classes of objects by unique characteristics, including color. Automatic scanning of an image for the presence of objects belonging to a particular class must allow for small variations in the characteristic color of the objects belonging to the class. Because real objects belonging to the class have a range of colors, rather than a single uniform characteristic color, they occupy a volume, rather than a single point, in a three-dimensional (3D) color space. Therefore, color ranges in the 3D color space may be defined, and if automatic scanning of an image detects colors within the range, the detection of an object belonging to the class may be registered.
The detection of a real class of objects by its color requires differentiating its characteristic color volume from color volumes of other objects. The characteristic color volume of a class of objects may be defined by digitizing the 3D color volume in color space. An object belonging to the class of object can then be detected by comparing the color of the object to a lookup table storing the digital representation of the 3D color volume. If each of the three colors defining the 3D color space is digitized to n bits, however, the lookup table of size n3 bits would be required to determine whether an object were in the predefined object class or not, and large lookup tables hinder the speed at which the image can be scanned.
Alternatively, the color volume of a class of objects can be defined by minimum and maximum color thresholds for each of the three color coordinates of a 3D color space, i.e. by defining a rectilinear color volume that includes the smaller arbitrarily shaped color volume characteristic of the object class. An object belong to the class may then be detected by comparing its color to the minimum and maximum thresholds that define the rectilinear color volume. Using minimum and maximum color thresholds to define a color volume requires the storage of only six parameter values, which permits faster scanning of images. Since the rectilinear color volume is larger than the actual characteristic color volume of the class of objects, however, objects that do not belong to the class of objects, but whose color is similar to the characteristic color of the class, may be falsely detected as members of the class.
A color threshold analyzer includes a converter to convert signals representative of a pixel color value, e.g., red (R), green (G), and blue (B) signals, to signals representing hue (H), saturation (S), and intensity (I) values. Comparators are provided to compare the hue value to upper and lower hue reference values, the saturation value to a lower saturation reference value, and the intensity value to upper and lower intensity values. A switch may be provided to select a desired orientation (i.e., clockwise or counter-clockwise) on a polar hue scale to define the values between the upper ad lower hue reference values.
A color identifier may output a signal indicating that the pixel color value corresponds to a desired color range in response to each of the H, S, and I values falling within their associated ranges.
The reference values may be analog or digital signals. Digital reference signals may be stored in registers associated with the comparators. Analog reference signals may be supplied to the comparators by digital-to-analog signals set from the bus of a host computer.
The color threshold analyzer may be implemented in hardware, software, or a combination of both.